My guess is that almost all the lines are occupied with active or waiting calls. When ACD (automatic call director) hits a certain threshold it starts the "call back later" message and dumps the calls until the backlog gets back under the threshold. Fortunately for those that have access to the Platinum lines, the call is "tagged" with the DNIS (dialed number inward service) number identifying it as a "premium customer" call and gets routed to the elite CSRs or queued ahead of regular calls when routed to regular CSRs. Part of the CRM system NW has installed.